Phoenix dust storm

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A dust storm moves northwest through Pinal County, Ariz., on July 18. A giant wall of dust was rolling through the Phoenix area, turning the sky brown, creating dangerous driving conditions, and delaying some airline flights. David Kadlubowski/The Arizona Republic/AP

A wall of dust moves through central Phoenix during a dust storm on July 18. The dust wall was about 3,000 feet high and created winds of 25 to 30 mph, with gusts of up to 40 mph, said Austin Jamison, a meteorologist with the National Weather Service. Ross D. Franklin/AP

A sign warns motorists of low visibility and high wind conditions in Phoenix on July 18. Michael Schennum/The Arizona Republic/AP

A dust storm rolls into the Phoenix area on July 18. Nick Oza/The Arizona Republic/AP

A vehicle drives through a brown cloud of blowing sand during a dust storm in Phoenix on July 18. Visibility was reportedly down to less than a quarter-mile in some areas. Ross D. Franklin/AP

A giant dust storm engulfs Phoenix, Ariz., on July 5. The massive storm reduced visibility and delayed flights as strong winds toppled trees and caused power outages for thousands of residents in the valley. Rob Schumacher/The Arizona Republic/AP

A dust storm known as a 'habub' rolls into downtown Phoenix on July 5, bringing strong winds and low visibility. Habubs are part of Arizona's annual monsoon season, which is now in full swing. Rob Schumacher/The Arizona Republic/AP

A large dust storm rolls across downtown Phoenix on July 5. ABC15.com/AP

Downtown Phoenix is covered by a dust storm on July 5. Amanda Lee Myers/AP

Motorists drive along Interstate 10 during a dust storm in Phoenix on July 5. Visibility was reduced to zero in some areas as wind gusts blew nearly 40 miles per hour, local media reported. Joshua Lott/Reuters

A truck drives through a dust storm in downtown Phoenix on July 5. Ross D. Franklin/AP

Motorists drive along Arizona State Highway 51 during a dust storm in Phoenix on July 5. Joshua Lott/Reuters

Mary Nichols and JoAnn Buckson (r.) run for cover as a dust storm blows through Phoenix on July 5. David Kadlubowski/Arizona Republic/AP

Customers sit outside a Starbucks Coffee cafe during a dust storm in Phoenix on July 5. Joshua Lott/Reuters

A dust-covered vehicle is parked outside Sky Harbor International Airport during a dust storm in Phoenix on July 5. Joshua Lott/Reuters

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